The field of art to which this invention pertains is dehydrogenation catalysts.
In the catalytic dehydrogenation of alkylaromatic hydrocarbons to alkenylaromatic hydrocarbons, e.g., the dehydrogenation of ethylbenzene to styrene, considerable efforts have been expended to develop catalysts which exhibit high conversion combined with high selectivity and increased stability.
Promoted iron oxide catalysts have been found to be especially useful in the dehydrogenation of alkylaromatic hydrocarbons to alkenylaromatic hydrocarbons. Typical commercial iron oxide-based dehydrogenation catalysts are generally promoted with the addition of other metal compounds, in the form of, but not limited to, oxides, hydroxides, carbonates, nitrates, etc. Often one of the promoters is an alkali metal compound with potassium being preferred. Other components may also be added to the dehydrogenation catalyst to provide further promotion, activation or stabilization. In all such dehydrogenation catalysts, minor amounts of modifiers are also typically present, such as organic burn-out agents: carbon black, graphite, methylcellulose, etc., which can beneficially effect the pore structure and/or other physical properties of the catalyst. In the discussion of the different metal groups, the reference will be based on the new IUPAC notation of the periodic table.
Typical catalysts used in dehydrogenation of saturated hydrocarbons to unsaturated hydrocarbons, as disclosed in U.S. Pat. No. 2,866,790, are iron oxide catalysts containing a small amount of chromium oxide as a stabilizer and a small amount of potassium compound as promoter. Improved catalysts according to this patent are made from iron oxide (39 to 47 weight percent), chromium oxide (1 to 10 weight percent), and potassium carbonate (51 to 59 weight percent).
Dehydrogenation catalysts having good physical strength are described in U.S. Pat. No. 2,866,791. These catalysts are made from 51 to 59 weight percent potassium fluoride, 1.0 to 10 weight percent chromium oxide with the balance being iron oxide (39 to 47 weight percent).
Catalysts designed for the dehydrogenation of alkylbenzenes, at elevated temperatures in the presence of steam, comprising iron oxide and as a promoter from about 1 to about 25 percent by weight of an alkali metal oxide, from about 1 to about 10 percent by weight of a rare earth metal oxide, and from about 0.1 to about 10 percent by weight calcium oxide, are disclosed in U.S. Pat. No. 4,749,674.
Another catalyst for the dehydrogenation of ethylbenzene to styrene disclosed in U.S. Pat. No. 5,510,552 contains at least one iron oxide, at least one bicarbonate, oxide or hydroxide of potassium and/or cesium, an oxide, carbonate, nitrate or hydroxide of cerium, a hydraulic cement, from about 0.2 to about 10 percent of a sodium oxide and from about 1.5 to about 20 percent calcium oxide.
WO 96/18458 discloses a method of preparing an iron oxide catalyst comprising contacting an iron oxide with a additive comprising an element selected from a large group of elements on the periodic chart, heating that iron oxide mixture to a temperature of at least about 600.degree., to afford structural rearrangement of the particle habit of said iron oxide, and then forming it into the catalyst. See also WO 96/18594 and WO 96/18593.
Similarly, U.S. Pat. No. 5,668,075 discloses the preparation of improved selectivity iron oxide dehydrogenation catalysts based on reconstructed iron oxides. The reconstruction of the oxides comprises contacting an iron oxide with a dopant substance comprising elements selected from a large group of components of the periodic chart and heating the doped iron oxide to a temperature of at least about 600.degree. C., preferably 800.degree. C. and 1100.degree. C. As in the previous references, rearrangement of particle habit is induced in iron oxide prior to it being formed into catalyst. Metal additives, disclosed in the teachings of the patent, are solely and specifically used to promote the physical transformation of the iron oxide and not the chemical properties of the catalyst formed based on the oxide.
Another dehydrogenation catalyst, which contains smaller amounts of iron oxide and relatively larger amounts of cerium oxide and potassium carbonate, is disclosed in U.S. Pat. No. 4,758,543. Catalysts having good activity and good selectivity are described in U.S. Pat. No. 3,904,552. These catalysts are made with iron oxide and alkali metal oxides plus molybdenum oxide and cerium oxide. Similar catalysts utilizing tungsten oxide in place of molybdenum oxide are described in U.S. Pat. No. 4,144,197.
Dehydrogenation catalysts which maintain high activity and selectivity over extended periods of time are described in U.S. Pat. No. 4,467,046. These catalysts contain iron oxide, an alkali metal compound, a cerium compound, a molybdenum compound and a calcium compound.
Improving stability of Fe/K/Ce/Mo/Ca/Mg oxide catalysts by incorporation of small amounts of chromium (100 to 5000 ppm) into the iron oxide prior to forming the catalyst is taught in U.S. Pat. No. 5,023,225.
The addition of titanium also results in improved activity and selectivity of iron oxide/potassium oxide catalytic systems, for ethylbenzene to styrene dehydrogenation, according to U.S. Pat. No. 5,190,906.
Dehydrogenation catalysts made from iron oxide, chromium oxide and kaolinite plus potassium oxide are disclosed in U.S. Pat. No. 4,134,858. The catalysts can also contain at least one oxide of copper, vanadium, zinc, magnesium, manganese, nickel, cobalt, bismuth, tin, or antimony.
U.S. Pat. Nos. 3,424,808 and 3,505,422 are directed to dehydrogenation catalysts which consist essentially of iron oxide, a minor amount of an alkali metal hydroxide or carbonate, and a minor amount of transition metal, preferably ruthenium, cobalt, or nickel.
Catalysts for the dehydrogenation of para-ethyltoluene to para-methylstyrene are described in U.S. Pat. Nos. 4,404,123; 4,433,186; 4,496,662; and 4,628,137. These catalysts are made with iron oxide and potassium carbonate, plus chromic oxide, gallium trioxide, or magnesium oxide. Each patent also discloses that the catalysts can optionally contain compounds of cobalt, cadmium, aluminum, nickel, cesium, and rare earth elements as stabilizers, activators and promoters. Other dehydrogenation catalysts and procedures for their use and manufacture are shown in U.S. Pat. Nos. 2,408,140; 2,414,585; 3,360,579; 3,364,277; and 4,098,723.
Dehydrogenation reactions are normally conducted at the highest practical throughput rates to obtain optimum yield. Yield is dependent upon conversion and selectivity of the catalyst.
Selectivity of the catalyst is defined as the proportion of the desired product, e.g., styrene, produced to the total amount of feedstock, e.g., ethylbenzene, converted. Activity or conversion is that portion of the feedstock which is converted to the desired product and by-products.
Improvements in either selectivity or activity can result in substantially improved operating efficiency. Higher activity catalysts, for example, would allow operation at lower temperatures than currently available catalysts, for any given conversion. Thus, in addition to high energy efficiency, the catalyst would be expected to last longer and generate less thermal by-products.
The ratio of benzene to toluene, B/T ratio, in the final product is another criteria to be used in determining effectiveness of the catalyst. The benzene by-product produced can be recycled for later processing. Toluene can not be easily recycled and is considered an undesirable by-product. Thus catalysts yielding higher B/T by-product ratio, all other factors the same, will be preferred.
There is thus a need for a dehydrogenation catalyst which has good selectivity and activity.
It is, therefore, an object of the invention to provide a novel dehydrogenation catalyst.
It is another object of the invention to provide an improved dehydrogenation catalyst having both high activity and selectivity.
It is another object of this invention to provide an improved catalyst for the conversion of ethylbenzene to styrene, with high activity and high selectivity.
It is another object of the invention to provide an improved dehydrogenation catalyst containing at least iron oxide, an alkali metal oxide, and a noble metal as a promoter.
It is another object of this invention to provide an improved dehydrogenation catalyst containing at least iron oxide, an alkali metal oxide, and rhodium and/or ruthenium and/or iridium and/or rhenium and/or osmium as a promoter.
It is another object of this invention to provide an improved dehydrogenation catalyst containing at least iron oxide, an alkali metal oxide and a noble metal, wherein the amount of the noble metal present in the catalyst is less than about 1000 ppm, preferably less than 100 ppm and most preferably less than 20 ppm.
It is still a further object of this invention to provide an improved process for the production of olefinic compounds, particularly styrene. These and other objects are obtained by the product and process of the present invention.